Coupling system



June 11, 1946.

H. T. FRHS COUPLING SYSTEM Filed March 17, 1942 TEAMS- L I G DE VICE INVENTOIR v H. 7? F Rl/S BVQZQ.

A 7'TORNEY Patented June 11, 1946 COUPLING SYSTEM Harald T. Friis, Rums on, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

YorlnN. Y., a corporation of New York Application March 17, 1942, Serial No. 435,017

8 Claims.

Q the copending applications of G. C. Southworth Serial No. 346,175, filed July 18, 1940, and A. C. Beck Serial No. 429,358, filed February 3, 1942, coupling between a wave guide and a line is ordinarily effected by inserting the line in the dielectric channel through a special aperture located at a point between the extremities or end orifices of the guide. In'the systems disclosed in the King patent and Southworth application the' allel impedances of the two branch dielectricchannels extending in opposite directions relative to the exciter. In the system of the Beck application, matching over a band of frequencies between the line and the total waveguide impedance is accomplished by omitting the criticalfrequency-tuners and by shieldinga portion of the exciter. Also, while in the single frequency systems of the King patent and the Southworth application an adjustable piston reflector positioned within the guide and spaced one-quarter wave-length from the exciter may be, and often is, utilized for the purpose of blocking one branch channel or, more accurately, for the purpose of converting without energy loss the bilateral wave propagation within the guide to a unilateral propagation, this arrangement cannot be employed for this purpose in the multi-frequency system of the Beck application because of the frequency limitation imposed by the one-quarter wave-length spacing mentioned above. Moreover, even in the single frequency system, a completely satisfactory impedance match and a conversion from bilateral to unilateral wave propagation in the guide, have not always been obtained because of the difficulty of critically adjusting the tuning pistons and the reflector piston, and of maintaining the proper adjustments.

It is one object of this invention to secure, in

- single frequency transmission-systems comprising a wave guide coupled to a line, unilateral wave propagation, within the guide without utilizing a reflecting piston.

It is another object of this invention to secure, in a multifrequenc transmission system comprising a wave guide coupled to a line, unilateral propagation in the wave guide.

It is still another object of this invention to match the impedances of a dielectric channel 2 and a conductive channel having substantially different impedances.

It is a further object of this invention to transfer energy between a coaxial line and a wavev guide, and over a wide carrier frequency microwave band, with minimumreflection loss.

It is also an object of the invention to couple dlfierent types of transmission channels for multifrequency operation without introducing reflection losses and without utilizing auxiliary ad'- justable apparatus.

As used herein, the term "transmission channel" is employed in a generic sense and includes a line or conductive channel and a dielectric or wave guide channel. Also, the comprehensive term quadrilateral includes rectangular and square; and the term rectangular is used in a narrow sense and excludes square."

In accordance with one preferred embodiment of the invention a coaxial line orv line channel having an impedance Z is connected to a quadri lateral wave guide or dielectric channel having a considerably larger impedance as, for example,

4Z, through a rectangular folded or looped wave guide coupling section having an impedance 22. The curvature of the folded wave guide section is in the plane of the short transverse dimension of the guide and the end apertures of the folded section are superimposed in a manner such that the short transverse dimensions of the end apertures are aligned. Stated differently, the looped wave guide section is bent or folded in the plane of polarization of the utilized wave component. The coaxial line is coupled through a matching device of the type disclosed in the copending application of A. C. Beck mentioned above to an intermediate point of the rectangular folded wave guide section; and the superimposed end apertures of the looped section are joined to an end orifice of the quadrilateral wave guide.

For multifrequency operation the coaxial line i is connected to the longitudinal center point of the rectangular loop section and the resulting two parts or branches of the loop section extending between the center point and the superimposed apertures include quadrature polarity changers, whereby the polarities of the utilized components or wavelets are rendered colinear in l branches differa half wave-length. ,By reason of the half wave-length difference the components propagated in the two loop branches and having at the exciter or coupling point a zero phase angle difference and identical polarities,

' placement of the coupling point relative to the above-mentioned longitudinal center point, is in a sense a compensation for the two oppositely directed quadrature changes produced in the polarities of the branch wav components by the two bendsor quadrants of opposite curvatures in the two branches. The combined characteristic impedances. of the superimposed loopapertures are serially associated and equal to the characteristic impedance, 42, of the quadrilateral guide.

In addition, the coaxial line impedance Z matched to that of the loop section connected thereto. I

The invention will be more fully from a perusal of the following specification taken in conjunction with the drawing on which like reference characters denotev elements of similar function and on which:

Fig. 1 is an elevational view 'of an embodiment of the-invention arranged for single frequency I operation; and

Fig, 2 is a perspective view of a difierent embodiment used for multifrequency operation.

Referring to Fig. 1, reference numeral 8 desig-.

nates a translation device for transmitting or receiving waves of a given frequency and numeral 2 denotes a conductive channel or coaxial line connected thereto. The line channel 2 is connected through a, rectangular wave guide section 3 folded or looped in the plane of its short transverse dimension a to a quadrilateral main wave guide or dielectric channel 6 and a radiating or collecting device such as horn 5. The line channel 2 is attached to the folded wave guide at a point 6 one-quarter wave-length removed from the longitudinal center point 1 of the folded wave guide 3 and is coupled thereto through a unifrequency-multifrequency coupling device of. the

type disclosed in the copending application of A. C. Beck mentioned above and comprising the adjustable sleeve member t.

Considering the impedance relations of the system of Fig. 1, the sleeve 8 is adjusted and a particular value for the short transverse dimension' a of the loop t is selected so that the ex-' posed portion 9 of the inner conductor of line,

2 has a length and impedance, as explained in the Beck application, such that the characteristic impedance Z of line 2 is matched at the single operating frequency to the total folded wave guide impedance comprising the two parallel impedances of the branches Id and ii.

Thus, assuming the line 2 has a characteristic impedance Z equal to 100 ohms, each of loop secimpedances are additive, the characteristic impedance of a rectangular wave guide channel being directly proportional to the short transverse dimension and substantially independent of the long transverse dimension, as disclosed in the copending application of G. C. Southworth menti of the apertures is 42, that is, equal to the input impedance or characteristic impedance at the main guided. Hence,. the folded guided consitutes an impedance transformer for matching I the main guide 4 to the line 2. I r

In operation, while the energies conveyed between the device I and the born 5, and propagated in the branches l and H of the folded section 3; flow relative to point-6 in oppositeor bilateral directions the combination including loop 3 functions to produce only unilateral propagation in understood the dielectric channel 4. Assuming that device I is a transmitter, the arrows M, i5, i6 and I1 denote the directions of propagation .respectively in line 2, branch l0, branch ii and guide a. The wavelets propagated in direction it and I6 have, at point 6, the same phase angle and are similarly polarized in the direction italigned with both the short transverse dimension a and the exposed exciter 9, that is, in'a horizontal direction included in the plane of the drawing. By reason of the oppositely curved portions or quadrants l9 and 20 in branches id and ii, respectively, the instantaneous polarities of these wavelets are rotated 90 degrees in opposite directions. At the two corresponding points 2! and 2? equally distantjfrom the superimposed apertures' i2 and I3, the wavelets have opposite phase angles, since the lengths of the two'paths extending between point 6 and points 28 and 22 difier by one-half wave-length; and in a sense, this opa is folded in the plane of its short transverse dimension 0. and the line and the folded guide are coupled through a unifrequency-multifrequency coupling device of the type disclosed in the abovementioned Beck application and comprising a sleeve t. The sidesor branches it and ii of the folded section 3 include, respectively. 90 degree polarity changers 25 and 2d, the twist or rotation of these polarity changers, relative to center point i, being of opposite sense. As in the system of Fig. 1, the main guide 3 is connected to an antenna such as a horn and the coaxial line 2 is connected to a translation device.

In operation, assuming the'system is used for transmittinggand that the translation'device is a multifrequency wave source, the sleeve 8 is adjusted to secure a substantially flat frequency-impedance match characteristic, as explained in the Beck application, whereby the impedance Z of the coaxial line is matched over a carrier frequency bandto the input impedance comprising the two impedances, 2Z and 22, of branches it and it connected in parallel. As in Fig. l, the serially connected impedance of apertures l2 and it, taken together, equal the input impedance sz of the main wave guide 5.

The translation device connected to line 2 funca above. Thus the total'iimpedance 2z+2z 7e point 1. the'polarity of wavelet it is rotated so degrees in a counter-clockwise direction and that of wavelet 28, 90 degrees in a clockwise direction by the polarity changers ream 25, respectively, so that at the corresponding points 29 and 3d equally distant from the superimposed apertures l2 and i3, these wavelets are oppositely polarized but have the same time phase angle. The wavelets are then oppositely rotated 90 degrees by the bent or curved portions i9 and 20 of branches l0 and Il and, at a second pair of corresponding points 3| and 32 equally distant from the superimposed apertures i2 and. [3, the wavelets 21 and 28 are in polarity agreement and therefore combine to produce a maximum vector resultant 33 in the guide 4. 16

Thus, in accordance with the invention, the system or combination illustrated by Fig. 2 and v comprising the multi-frequency coaxial line-wave guide coupling device, and a folded wave guide section including the oppositely twisted or rotated polarity changers and having its two apertures superimposed and joined to the end orifice of a main dielectric channel, functions to match overa band of carrier frequencies including several hundred megacycles, the impedances' of a'conductive channel and a dielectric channel which impedances may be greatly difierent. At the same time the system produces unilateral or one-way propagation in the main dielectric channel.

Although the invention has been explained in connection with certain embodiments thereof it should be understood that it is not to be limited to these arrangements inasmuch as other apparatus may be employed in successfully practicing the invention. More particularly, the folded wave guide coupling section and the main wave guide may each have a square instead of a rectangular cross section. Also, any other type of line channel, such as a two-wire balanced line and even a dielectric wave guide channel, may be substituted for the coaxial line 2, and the invention may be utilized for coupling two dielectric channels or for coupling a balanced linechannel to a main wave guide channel.

What is claimed is: r

1. In, combination, a coaxial line having a given impedance and an inner conductor and an outer conductor, a wave guide having a different impedance, and means for coupling said line and guide and producing unilateral propagation .in said guide comprising a rectangular wave guide looped section having an impedance intermediate said impedances, the end openings of said loop section being superimposed and connected to the .having -an input impedance Z,-a line conductor having a characteristic impedance a coupling wave guide looped section; having a characteristic impedance I said conductor being ca died to a intermediate point in said'coupling section and the end openings ofsaid section being superimposed and Joined to one end opening ofsaid first guid v whereby reflection losses along said system are eliminated and the wave propagation in said first wave guide is unilateral.

3. In combination, a main rectangular dielectric channel having a short transverse dimension, a conductor channel, said channels having different impedances, and a transformer for matching said impedances comprising a plurality of rectangular dielectric branch channels, each of the last-mentioned channels having a short transverse dimension equal to one-half of said firstmentioned short dimension and being connected between the conductor channel and said main diguide and comprising a conductor extending within said guide along said short transverse dimension, the rectangular guide branches included between said mid-point and the quadrilateral same polarity at the junctionpf said orifice and said superimposed apertures.

5. In combination, a' firstrectangular wave guide having an end orifice, a coaxial line comprising two conductors, said line and guide having diflerent impedances, an impedance matching transformer included between said guide and line and comprising a second rectangular wave openings at both ends, said coaxial line connected .to said second guide at an intermediate point thereof and extending within the guide in a direction coincident with the shorter transverse -guide dimension, said second guide being folded in the: plane of the shorter dimension and having itsopenings superimposed and connected to said orifice.

-6. A combination in accordance with claim 5, the lengths of the branches extending between said intermediate point and said openings being equal.

'7. A combination in accordance with claim 5, the length of the branchincluded between said intermediate point and one of said openings being a half wave-length or a multiplejthereof greater than the length of the branch extending between said point and the other of said openings.

8. A quadrilateral dielectric wave channeltransmission line coupling device comprising'a folded rectangular wave guide having a short" transverse dimension equal substantially to onehalf of the short transverse dimension of said channel, means for energizing said guide with.

transverse electric H11 waves, said guide bein folded in the' plane of polarization of said waves,

said folded guide having its end apertures superimposed for junction with said'channel and an aperture at an intermediate point for junction with said line, and the two guide branches included between said intermediate aperture and said superimposed end apertures being oppositely twisted degrees. 1 V V a na I 

